(1) Field of the Invention
The present invention relates to a thrust bearing and a bearing device that receive an axial force of a crankshaft of an internal combustion engine.
(2) Description of Related Art
A crankshaft of an internal combustion engine is rotatably supported, at its journal portion, by a lower part of a cylinder block of an internal combustion engine via a main bearing which is configured by assembling a pair of half bearings into a cylindrical shape.
One or both of the pair of half bearings is used to be combined with a half thrust bearing which receives an axial force of the crankshaft. The half thrust bearing is provided at one or both of axial end surfaces of the half bearing.
The half thrust bearing receives the axial force generated in the crankshaft. That is, the half thrust bearing is placed for the purpose of bearing the axial force applied to the crankshaft when the crankshaft is connected to a transmission via a clutch, for example.
On a sliding surface side of the half thrust bearing close to both circumferential ends thereof, thrust reliefs are formed so that a bearing member becomes thinner toward the respective circumferential end surfaces. In general, the thrust relief is formed so that a length from the circumferential end surface to the sliding surface of the half thrust bearing, and a depth at the circumferential end surface are constant irrespective of the position in a radial direction. The thrust relief is formed in order to absorb misalignment of the end surfaces of the pair of half thrust bearings when mounting the half thrust bearings on a split type bearing housing (see FIG. 10 of JP-A-11-201145).
The crankshaft of the internal combustion engine is supported, at its journal portion, by the lower part of the cylinder block of the internal combustion engine via the main bearing consisting of the pair of half bearings. Here, lubrication oil is fed from an oil gallery in a wall of the cylinder block through a through hole in a wall of the main bearing into a lubrication oil groove formed along an inner circumferential surface of the main bearing. The lubrication oil is supplied to the lubrication oil groove of the main bearing in this manner, and then supplied to the half thrust bearings.
In general, a laminated structure in which an aluminium bearing alloy layer or a cupper bearing alloy layer is formed on one surface of a steel back metal is used for a thrust bearing which receives an axial force of a crankshaft of an internal combustion engine. Further, there is proposed a thrust bearing improved in conformability, fatigue resistance or load carrying capacity by applying a resin slide layer on the aluminium bearing alloy layer or the cupper bearing alloy layer (see JP-A-H07-238936). As a material used for the resin slide layer, there is a material in which a solid lubricant is added to a resin obtained by polymer-alloying a heat-resistant resin such as polyamide imide having high strength and excellent heat resistance with polyamide or the like (see JP-A-2008-308595).
Meanwhile, in recent years, oil pumps for supplying lubrication oil of internal combustion engines have been reduced in size, so that the amount of lubrication oil to be supplied to the bearings decreases. Accordingly, the amount of lubrication oil leaking through the end surfaces of the main bearing tends to decrease, and the amount of lubrication oil supplied to the half thrust bearings also tends to decrease. To address this, there is proposed an art for improving retainability of lubrication oil by forming a plurality of narrow grooves in parallel on the sliding surfaces of the half thrust bearings, for example (see JP-A-2001-323928).